Recently, electronic apparatuses with a microcomputer built therein are smaller in size. During operation of a known small-sized electronic apparatus, a memory board is attached in a memory slot of a microcomputer board with the CPU or system logic mounted thereon.
Presently, such memory board is a main memory of the CPU and is provided with a dynamic random access memory (hereinafter referred to as D-RAM) which is small in size and large in capacity. In the D-RAM, row and column addresses are arranged and one address is designated in a matrix manner. Therefore, the system logic has therein a logic for classifying an address signal transmitted from the CPU into the row address and the column address.
The system logic also has therein an interleave logic in which, for efficiently accessing the D-RAM, the D-RAM is divided into a plurality of banks, and an address signal transmitted from the CPU is converted such that adjoining addresses are allotted to individual banks.
However, since the memory in D-RAM is lost when power supply is disconnected, data cannot be stored in the aforementioned memory board. Therefore, a need exists for a memory board that can store data even when the power supply is disconnected.
To fulfill such need, an erasable and programmable read only memory (hereinafter referred to as EP-ROM) can be mounted on the memory board. However, EP-ROM requires ultraviolet radiation for deleting data, all the data is deleted at once, and thus EP-ROM cannot be partially written or erased.
These days a nonvolatile flash memory that can be partially written or erased is desired. However, in the flash memory, addresses are allotted contiguously and data is processed at an insufficiently high rate for the main memory of CPU.